I think we're underestimating the PRESS in this discussion.
In 2004 Howard Dean was running an excellent center-left, anti-war campaign, leading the media and DLC-preferred candidate John Kerry.
Then came "the scream." It was nothing but the media and the Dem power brokers instantly blew it way out of proportion to destroy Dean. It was all they had and they milked it for all it was worth.
As of now, a few in the media have called for Biden to withdraw from the race. But despite 100 times the provocation, there's no firestorm.
Why the difference? All I can think of is that Biden is the insider's choice; whereas Dean was an upstart. Sort of like the Hillary vs Bernie situation.